Discretized valve state control for multi-level hydraulic systems

Abstract

An actuation pressure to actuate one or more hydraulic actuators may be determined based on a load on the one or more hydraulic actuators of a robotic device. Based on the determined actuation pressure, a pressure rail from among a set of pressure rails at respective pressures may be selected. One or more valves may connect the selected pressure rail to a metering valve. The hydraulic drive system may operate in a discrete mode in which the metering valve opens such that hydraulic fluid flows from the selected pressure rail through the metering valve to the one or more hydraulic actuators at approximately the supply pressure. Responsive to a control state of the robotic device, the hydraulic drive system may operate in a continuous mode in which the metering valve throttles the hydraulic fluid such that the supply pressure is reduced to the determined actuation pressure.

What is claimed is: 
     
       1. A method comprising:
 receiving, at a control system of a legged robot, a first indication that a leg of the legged robot is in contact with a ground surface during movement of the leg according to a gait pattern; 
 based on the received first indication:
 selecting, by the control system, a first pressure rail among a set of pressure rails, each pressure rail in the set of pressure rails associated with a different respective supply pressure; and 
 supplying, by the control system, pressurized hydraulic fluid at a first supply pressure via the first pressure rail to a hydraulic actuator associated with the leg, the pressurized hydraulic fluid at the first supply pressure causing the hydraulic actuator to generate a liftoff load configured to push the leg against the ground surface; 
 
 receiving, at the control system, a second indication when the leg of the legged robot lifts off the ground surface; and 
 based on the received second indication:
 switching, by the control system, from the first pressure rail to a second pressure rail among the set of pressure rails; and 
 supplying, by the control system, the pressurized hydraulic fluid at a second supply pressure via the second pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the second supply pressure causing the hydraulic actuator to raise the leg away from the ground surface to a raised position, 
 
 wherein the second supply pressure is less than the first supply pressure. 
 
     
     
       2. The method of  claim 1 , further comprising:
 while supplying the pressurized hydraulic fluid at the second supply pressure via the second pressure rail to the hydraulic actuator, receiving, at the control system, a third indication when the leg of the legged robot reaches the raised position; and 
 based on the received third indication:
 switching, by the control system, from the second pressure rail to a third pressure rail among the set of pressure rails; and 
 supplying, by the control system, the pressurized hydraulic fluid at a third supply pressure via the third pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the third supply pressure causing the hydraulic actuator to step the leg of the legged robot in a first direction relative to the ground surface, 
 
 wherein the third supply pressure is less than the second supply pressure. 
 
     
     
       3. The method of  claim 2 , further comprising, after hydraulic actuator causes the leg of the legged robot to step in the first direction:
 switching, by the control system, from the third pressure rail to a fourth pressure rail among the set of pressure rails; and 
 supplying, by the control system, the pressurized hydraulic fluid at a fourth supply pressure via the fourth pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the fourth supply pressure causing the hydraulic actuator to set the leg of the legged robot in contact with the ground surface. 
 
     
     
       4. The method of  claim 3 , wherein the fourth supply pressure is less than the third supply pressure. 
     
     
       5. The method of  claim 1 , wherein each different respective supply pressure is associated with a respective portion of the gait pattern. 
     
     
       6. The method of  claim 5 , wherein the gait pattern comprises:
 a first portion corresponding to when the leg of the legged robot pushes against the ground surface using the liftoff load; 
 a second portion corresponding to when the leg of the legged robot raises away from the ground surface to the raised position; 
 a third portion corresponding to when the leg of the legged robot steps in the first direction relative to the ground surface; and 
 a fourth portion corresponding to when the leg of the legged robot sets in contact with the ground surface. 
 
     
     
       7. The method of  claim 1 , further comprising:
 receiving, at the control system, environment data indicative of one or more physical features of an environment about the legged robot; and 
 determining, by the control system, that the environment data corresponds to even terrain within the environment about the legged robot, 
 wherein supplying the pressurized hydraulic fluid at the first supply pressure comprises supplying the pressurized hydraulic fluid at the first supply pressure via the first pressure rail to the hydraulic actuator un-throttled. 
 
     
     
       8. The method of  claim 1 , further comprising:
 receiving, at the control system, environment data indicative of the ground surface being uneven; 
 generating, by the control system, a tolerated pressure difference based on the environment data; 
 determining, by the control system, whether a pressure difference between an actuation pressure to actuate the hydraulic actuator to generate the liftoff load and the first supply pressure exceeds the tolerated pressure difference; and 
 when the pressure difference exceeds the tolerated pressure difference, throttling, by the control system, a flow of the pressurized hydraulic fluid from the first pressure rail to the hydraulic actuator. 
 
     
     
       9. The method of  claim 1 , further comprising:
 receiving, at the control system, environment data indicative of the ground surface being uneven; 
 generating, by the control system, a tolerated pressure difference based on the environment data; 
 determining, by the control system, whether a pressure difference between an actuation pressure to actuate the hydraulic actuator to raise the leg away from the ground surface to the raised position and the second supply pressure exceeds the tolerated pressure difference; and 
 when the pressure difference exceeds the tolerated pressure difference, throttling, by the control system, a flow of the pressurized hydraulic fluid from the second pressure rail to the hydraulic actuator. 
 
     
     
       10. The method of  claim 1 , further comprising, supplying, by a hydraulic drive system of the legged robot, the first supply pressure to the first pressure rail and the second supply pressure to the second pressure rail. 
     
     
       11. A robot comprising:
 a frame; 
 a leg coupled to the frame and configured to rotate relative to the frame; 
 a hydraulic actuator coupled to the leg and configured move the leg in a gait pattern relative to the frame; 
 a set of pressure rails configured to selectively supply hydraulic pressure to the hydraulic actuator, each pressure rail of the set of pressure rails associated with a different respective supply pressure; and 
 a control system configured to:
 receive a first indication that the leg is in contact with a ground surface during movement of the leg according to the gait pattern; 
 based on the received first indication:
 select a first pressure rail among the set of pressure rails; and 
 supply pressurized hydraulic fluid at a first supply pressure via the first pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the first supply pressure causing the hydraulic actuator to generate a liftoff load configured to push the leg against the ground surface; 
 
 receive a second indication when the leg of the robot lifts off the ground surface; and 
 based on the received second indication:
 switch from the first pressure rail to a second pressure rail among the set of pressure rails; and 
 supply the pressurized hydraulic fluid at a second supply pressure via the second pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the second supply pressure causing the hydraulic actuator to raise the leg away from the ground surface to a raised position, 
 
 wherein the second supply pressure is less than the first supply pressure. 
 
 
     
     
       12. The robot of  claim 11 , wherein the control system is further configured to:
 while supplying the pressurized hydraulic fluid at the second supply pressure via the second pressure rail to the hydraulic actuator, receive a third indication when the leg of the robot reaches the raised position; and 
 based on the received third indication:
 switch from the second pressure rail to a third pressure rail among the set of pressure rails; and 
 supply the pressurized hydraulic fluid at a third supply pressure via the third pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the third supply pressure causing the hydraulic actuator to step the leg of the robot in a first direction relative to the ground surface, 
 wherein the third supply pressure is less than the second supply pressure. 
 
 
     
     
       13. The robot of  claim 12 , wherein after hydraulic actuator causes the leg of the robot to step in the first direction, the control system is further configured to:
 switch from the third pressure rail to a fourth pressure rail among the set of pressure rails; and 
 supply the pressurized hydraulic fluid at a fourth supply pressure via the fourth pressure rail to the hydraulic actuator, the pressurized hydraulic fluid at the fourth supply pressure causing the hydraulic actuator to set the leg of the robot in contact with the ground surface. 
 
     
     
       14. The robot of  claim 13 , wherein the fourth supply pressure is less than the third supply pressure. 
     
     
       15. The robot of  claim 11 , wherein each different respective supply pressure is associated with a respective portion of the gait pattern. 
     
     
       16. The robot of  claim 15 , wherein the gait pattern comprises:
 a first portion corresponding to when the leg of the robot pushes against the ground surface using the liftoff load; 
 a second portion corresponding to when the leg of the robot raises away from the ground surface to the raised position; 
 a third portion corresponding to when the leg of the robot steps in the first direction relative to the ground surface; and 
 a fourth portion corresponding to when the leg of the robot sets in contact with the ground surface. 
 
     
     
       17. The robot of  claim 11 , wherein the control system is further configured to:
 receive environment data indicative of one or more physical features of an environment about the robot; 
 determine that the environment data corresponds to even terrain within the environment about the robot; and 
 supply the pressurized hydraulic fluid at the first supply pressure via the first pressure rail to the hydraulic actuator un-throttled. 
 
     
     
       18. The robot of  claim 11 , wherein the control system is further configured to:
 receive environment data indicative of the ground surface being uneven; 
 generate a tolerated pressure difference based on the environment data; 
 determine whether a pressure difference between an actuation pressure to actuate the hydraulic actuator to generate the liftoff load and the first supply pressure exceeds the tolerated pressure difference; and 
 when the pressure difference exceeds the tolerated pressure difference, throttle a flow of the pressurized hydraulic fluid from the first pressure rail to the hydraulic actuator. 
 
     
     
       19. The robot of  claim 11 , wherein the control system is further configured to:
 receive environment data indicative of the ground surface being uneven; 
 generate a tolerated pressure difference based on the environment data; 
 determine whether a pressure difference between an actuation pressure to actuate the hydraulic actuator to raise the leg away from the ground surface to the raised position and the second supply pressure exceeds the tolerated pressure difference; and 
 when the pressure difference exceeds the tolerated pressure difference, throttle a flow of the pressurized hydraulic fluid from the second pressure rail to the hydraulic actuator. 
 
     
     
       20. The robot of  claim 11 , further comprising a hydraulic drive system communicating with the control system to supply the first supply pressure to the first pressure rail and the second supply pressure to the second pressure rail.